Telephone system of the relay type



Aug. 5, 1958y Y F. sPlx-:CKER ETAL 2,845,510

TELEPHONE SYSTEM oT THE RELAY TYPE 4 SheetsSheel'. l

FiledA June 18. 195s QON ONKJ QN xmms wie A NWUJN.N.

@xd A @Lunch Luck A118' 5, `1958 F. sPlEcKER ETAL K 2,846,510

TELEPHONE SYSTEM OF THE RELAY IYPE Filed June 18. 1953 4 Sheets-Sheet 2 Tnucsfvav maar? Y LK4 LKt Tn l Fig. 2

Tn Gr 1 Aug. 5, 1958 F. sPlEcKr-:R ETAL l 2,846,510

TELEPHONE sYsTEM oE THE RELAY TYPE xfiled June 18, 1953 4 Sheets-Sheet 3 F 6. .3a

INVENTORS FRIEDRICH SPIECKER '8 FRITZ LUBBERGER; deceased, by Emma Lubberger, sole heir Aus- 5, V195s ESPIECKER my 2,846,510

TELEPHONE SYSTEM OF THE RELAY TYPE FRlEDRICH SPIECKER a FRITZ I LUBBERGER; deceased, by Emma Lgb ger, sole heir AHV United States Patent O TELEPHNE SYSTEM F 'II-EE RELAY TYPE Friedrich Spiecker, Berlin-Charlottenburg, Germany, and Fritz Lubberger, deceased, late of Emmendingen, Germany, by Emma Lubherger, sole heir, Emmendingen, Germany, assigner-s to Siemens & Halske Aktiengesellschaft, Munich and Berlin, Germany, a corporation of Germanyl Application .lune 18, 1953, Serial No. 362,442

Claims priority, application Germany January 9, 1950 Claims. (Cl. 179-18) This invention relates to telecommunication and is particularly concerned with a telephone system employing relay selectors.

In signal communication, particularly telephone systems, optimum utilization of the trunk lines and linking equipment is obtained if a large number of them can be made available to a large group of incoming lines for common use. ln large exchanges, therefore, the subscribers lines are combined into main groups of 1000 or 2000 lines each. Each subscribers line of such a main group is given access, by means of a dual preselection, to each of the tirst group selectors available to the group as a whole.

The invention relates to telecommunication, particularly telephone systems employing relay selectors. The object of the invention is to obtain also in this case the most complete possible utilization of the linking equipment connectible with calling subscribers lines; and the invention accomplishes this by making it possible for each line of any subgroup, from among the groups combined into a main group of incoming lines, to be connected with any of the linking devices, associated with the main group as a whole, by means of at least three linking devices consisting exclusively of connecting relays, while allotters arranged between the individual connecting devices determine which of the links is to be used at a given time in establishing the call connection.

In one known system, a main group of 1000 subscribers lines has associated therewith a large number (80) of trunk lines to which dial pulse registers are connected. The trunk lines are subdivided into a plurality of junction groups. The main group of subscribers lines is subdivided into 20 groups of 50 lines each. To each group is available a definite number (6) of primary links. Each primary link has access to two secondary links. In order to obtain in this system as uniform a distribution of the trac as possible, the relatively few (l2) secondary links accessible to a group of 50 subscribers lines are multipled with an equal number (12) of trunk lines from the individual junctions by means of cross-connecting jumpers. In this system, each subscribers line does not have access to each linking device. Thus it may happen that notwithstanding availability of idle trunk lines, a calling subscriber may not be able to reach one of them. This disadvantage is avoided by the present invention.

The accompanying drawings illustrate two embodiments of the invention, but the latter is not limited to these embodiments. For heavier or lighter trac, the grouping of the links may be varied. The number of links in the individual groups and subgroups may vary. Furthermore, it is possible to use more than three connecting fields in series.

Figs. l and 2 illustrate grouping schemes for the preselection stage of a main group of 1000 subscribers lines; and

Figs. 3a and 3b, placed side by side with marked lines in alignment, show the circuit for the nders and allotters of the preselection stage.

It is assumed that the subscribers lines are combined in subgroups of 50 lines each. Pour such subgroups constitute one group. Fig. l1 shows subgroups TnUGri to TnUGr4 that constitute group TnGrl, and also shows subgroups TnUGr17 and TnUGr20 forming part of group TnGrS.

Each subgroup has associated therewith a line finder LK through which the subscribers lines can be coupled with subscribers links ZLt. For a predetermined amount of traine, the 50 subscribers lines of a subgroup require l0 links. The subscribers links are two-way links, that is they are used for both incoming and outgoing traffic. Not all subscribers links need be two-way, but some (for example two) may serve exclusively for outgoing traffic and some (for example two) solely for ,incoming trac.

The making-available of an idle subscribers link takes place in link allotters LO, one of which is associated with each subgroup of lines. In the link allotter, each two-way link divides into two branches. One branch is provided for outgoing traic; it constitutes the rst link of the preselection stage and is designated lZLv. The other branch constitutes the last link of the nal selection stage. If three linking stages are required for the final selection stage, then this second branch constitutes a link 3.ZLe; it has been indicated in all link allotters shown in the drawings. In incoming trailic, the subscribers links are called into play in the reverse sequence to that applying to outgoing tratilc. Therefore, the incoming-traffic branch of link ZLzl constitutes link 3.ZLe1, the branch of ZLI9 is 3.Zl.e2, and so forth.

The main group of subscribers lines as a whole has sixty switching devices WRl to WR60 allotted thereto. These switching devices, hereinafter referred to as selector relay sets, include the feed and impulse bridges. A selector relay set used by a calling subscribers line is connected by a finder to a digit pulse register (translator). This register consists of groups of digit storing relays controllable by dial impulses. The selector relay sets, iinders, translators, etc. of the dialing circuit are not shown in the drawings as the invention is concerned only with the preselection stage up to the selector relay sets. Sutlice it to say that in installations comprising more than 1000 subscribers lines, the connections, apart from the preselection stage, are advantageously built up in two selection stages, viz., a group selection stage and a nal selection stage.

To insure maximum utilization, each of the sixty selector relay sets associated with the main group of subscribers lines must be accessible to any subscribers line regardless of the group or subgroup to which the line belongs. ln the embodiment illustrated in the drawings, this is accomplished by giving each primary link LZLV access to two groups of selector relay sets WR, but not to all sets, via two connecting fields, viz., a preselection primary nder VZK and a preselection tiual nder VNK. The saving of connecting relays brought about by the invention is so substantial as to have a noticeable eiect upon the cost of the installation as a whole- It each primary link, that is, each 1.211, were to be given access through a connecting eld to all selector relay sets, each link 1.ZLv would have to have sixty connecting relays. With 20 subgroups of subscribers lines each having 10 primary links, making a total of 200 links 1.ZLv, this would require as many as 12,000 connecting relays. To these must be added the connecting relays required inthe line finders.

An installation requiring, in the preselection stage alone,

22 connecting relays for each subscribers line, viz., 10 relays provided for the individual lines in the line finder, and 12 relays constituting its share in the 12,000 connecting relays of the second preselection stage, certainly is far from economical.`

The number of connecting-relays is reduced vvery substantially-to %-by giving each primary link 1.ZLv access through aconnecting eld to only a limited number of selector relay sets. With-60 selector relay sets being required to cope with the presupposed volume of trahie, if each subscriber is to be able to reach all selector relay sets, and if a subgroup of lines has ten links 1.ZLv available, each 1.ZLv link must be`able to reach a group of six selector relay sets. With'` 200 primary links this calls for 1200 connecting relays.

The use, according to the invention, of at least tvvo connecting fieldsl apart from theV line nders, results in an even further reduction of the number of connecting relays. kIn the installation according to Fig. l, a total of only 700 connecting relays is required for the second and third stages of preselection in a group of 1000 lines. This amounts to only 0.7 relay per subscriber.

For each group of lines, there are provided 'Z0 secondary links (group links) 2.ZLv. Thus, groupTnGrl has links 2.ZLv1 to 2.ZLv29, and group TuGI-S has links 2.ZLv81 to 2.ZLv100. Accordingly, there are twice as many group links 2.ZLv per group of lines as there are primary links 1.ZLv per subgroup.

The selector relay sets WR are subdivided into as many groups as there are group links per group of lines, that is, in the present case. Accordingly, with.60 selector relay sets, each group link has access to a group consisting. of three selector relay sets. For example, 'link 2.ZLv1 of group TnGrl, link 2.ZLv81 Vof group TnGrS, and links 2.ZLV21, 2.ZLv41 and 2.ZLv61 (the last three not. shown) of groups TnGrZ, TnGr3 and TnGr4, respectively, have access to selector relay sets WRI to'WRS; links 2.ZLv2, 2.ZLv82, etc., have access tonWR4 to WR6,

andso forth. The Vconnection of a group link 2.ZLv to a selector relay set is effected in a finder VNK, one of thesebeing provided per group of lines. Thus, group TnGrl has finder VNKI, group TnGrZ has Vfinder VNKZ, and group TnGrS has nder VNKS associated therewith.

Each primary link 1.ZLv has accessV to two 'group links 2.ZLv; for example, primary vlink 1.ZLv1to group links 2.ZLv1 and 2.ZLv2. VNow since, -as` explained above, each group link 2.ZLv can reach three selector relay sets, each V1.ZLv link has access to six sets. Each 1.ZLv link of a subgroup reaches a diierent pair -of groupY links. This has the result that each subscribers line can be connected with any one of the sixty selector relay sets ac'- cessible to the totality of thersubscriber groups. Y

Each preseleetion primary finder VZK'has 10X-2, or 20 connecting relays. this amounts to 400 relays. Each preselection iinal iinder VNK of the ve line groups has 20 3 vor 60 connecting relays, so that there are a total of 300 connecting relays in the preselection iinal finders. Thus, as already mentioned, a total of only 400 plus 300, or 70() relays is required for all preselection primary and final finders of a main group of lines.

Between the preselection final finder VNK' fof each group and the preselection primary iinders VZKfofthe same group, an allotter VI-IO is interposed, serving to control the availability of the group'links 2.ZLv; By controlling blocking relays in the link allotters LO of each subgroup TnUG, `the allotter VHO prevents an idle primary link, such as 1.ZLv1,.from being made available even though the associated group linksZZLvland 2.ZLv2 may be idle, whenever the selector relay sets WRI to WR6v accessible tothesev group links arein use by subscribers Vfrom other line groups and are. thus blocked. Y How this is done. specifically, will be lexplained with reference to Figs. Saand 3b:

YFor trahie that issheavieror,lighter than that forming the basis ofthe telephone system according to Fig. 1, the number of group links available to a subscriber group will not always be a straight multiple of the number of primary links 1.ZLv assigned to a subgroup of subscribers lines. Also,-to carry the trafc of a main group of subscribers lines may "require a number ofl selector relay sets which again is not a straight multiple of the number of group links of a line group. f- For example, to cope with a certain amount of traffic, one main group of lines may require 45 selector relay sets. For each line group, 15 group links 2.ZLv must be provided. All line subgroups would -be equipped uniformly with primary links, and even those subgroups which carry but light traic,.wou1d have 10 primary links 1.ZLv.

Now it would be possiblev to give each. group linkaccess to three selector relay sets, but this would require that ve of the ten primary links be coupled in the preselection primary iinder with one group link each,-while the other tive links would'have `to be coupled with two group links each. Such grouping,l however, is undesirable frorn the point of view of back-blocking, because the primary links 1.ZLv connectible with but one group link will frequently be blocked since these group links will be in useby subscribers lines from other subgroups.

Therefore, vaccording'to the invention, the number of group Vlinks is increased above the number inherently required,so that each primary link 1.ZLv has access to at least two group linksr2.ZLv. Thus, instead of fteen, there are twenty group links. The five links that would not theoretically be needed to cope with the tratc, have the further eEect of preventing blocking of the tra'ic in one group by back-blocking from the other groups.

' The number of group links is a straight multiple (2). of

the number of primary links per subgroup. The twenty group links will then have access to the 45 ,selector relay sets. How the'latter are assigned tothe group links is illustrated in Fig. 2. Five group links, vfor example 2.ZLv1, 2.ZLv5, 2.ZLv'9, 2.ZLv13 and 2.ZLv17,`are given access to three'selector relay sets each while each of the remaining fteen group links will have access to two selector relay sets. The connecting relays required for each line group with this manner ofl grouping are as follows: p Y

In the four preselection primary finders, there areV 4 2 10 or 80 connecting relays; Vthe preselection nal nder of this line group contains l5 2 plus 5X3, or a total of 45 relays; thus, the total is 125 connecting relays i for a group of 200 lines.

This number of connecting relays for a `group of 200 lines is but insigniticantly higher lthan the number that would be required in the above-mentioned arrangement with 15 group links, since the number of connecting re- With ive times four finders VZK lays 4in the preselection final finder would again beV 45, as each of the 15 group links must be equipped With three connecting relays. Each preselection primary finder would require only l5 connectingrelays since the ten primary links 1.ZLv have access to only 1'5 group links;

traic of a linegroup,` 17...'groups can be formed withV two relay sets each, and three groups with three relay sets each.V In that case, three of the twenty group links 2.ZLv, kfor example, the 1st, 8th .and 15th, would have access to three relay sets each, while the remaining seventeen links haveiaccess totWo selector relay sets each.

Thus, accordingV to the invention, Vthe' most favorable conditions are obtained by giving each primary link;

1.ZLv access to at least two group links and by subdividing those selector relay sets which are at the disposal of an entire main group of subscribers lines consisting of a plurality of line groups, into groups of as nearly as possible equal size, so that the number of selector relay sets for the individual groups does not differ by more than one.

Fig. 3a shows the equipment of two subscribers lines T111 and T112. Assume a call is made effective on line T111. Loop closure upon lifting the receiver, operates the line relay AR1 in the subscriber relay set TRS. Contact lari of this relay disconnects the control lead m1 from the line contact bank lof the circuit of the tina] selection stage, while contact 21111 of the relay AR1 closes the following circuit:

(l) Plus, contacts 3pl01, 40111, relay R1, lead 5, contact 2ar1, winding Il of finder starting relay Kal, contact 6tr1, winding l of relay Kal, lead 7, relay Anl, Minus.

Relay R1 closes a holding circuit at contact Sarl that is independent of contact 40111. The finder starting relay Kal by its contact 91u11 short-circuits its own winding II and thus prevents a new iinder start from being initiated in the event that prior to connection of line T111 to one of the selector relay sets another call should come in on another line such as T112. If relay ARZ were to operate and close contact 10m-2, the lnder starting relay Ka2 could not operate since short-circuiting or' the high-resistance winding II of relay 1(01 diverts the current from relay Ka2. Closure of contact 11ka1 produces the nder start by connecting positive battery to the windings I of all connecting relays K11, K12 K11o of line T111. Contact 121ml prepares the holding circuit that is to be completed after switching through to one of the selector relay sets.

The relay R1 of the link allotter L01 is the directionindicating relay. Its actuation indicates that the finder start originates from a calling line, so that an outgoing connection is to be established in which that branch of the selected subscribers link ZLt which constitutes a primary link 1.ZLv of the preselection stage, is to be switched through. The indication of direction takes place through opening of contacts 1311 and 14r1, and closure of contacts 151-1 and 1611. This causes Cutting out of those relays (Q01, QeZ, etc.) and relay windings (C111,

C211, etc.) which are to be effective in incoming calls only. At the same time those relays (Qv1, Qv2, etc.) and relay windings (C11, C21, etc.) are made effective which are required for completing outgoing connections. Operation of relay A111 initiates the making-available of an idle subscribers link ZL.

Let us assume that the subscribers links ZLtl ZLIZ are idle. As determined by a contact chain, link ZLt1 is the one to be used rst. But before this link may be made available, it must i'lrst be ascertained whether an idle selector relay set WR can be reached through this link, or more specifically through its branch 1 ZLv1. As is evident from Fig. l, branch 1.ZLv1 has access to two groups of selector relay sets WRl to WR3 and WR4 to WR6. Whether one of these relay sets is idle is ascertained by relay C1, serving as a blocking relay.

if the selector relay sets WR of both groups are blocked, then the blocking contacts 1701, 1802, 1903 of one group, and 2904, 2105 and 2206 of the other group are closed. ln all group allotters VI-101 to VHCS, blocking relays are energized by circuits by-passing the finders VNK1 to VNKS. Thus, in allotter Ytf1-101, the blocking relays C11 and C12 are energized as follows:

(2) Plus, contacts 1701, 1802, 1903, lead 23, winding I of relay C11, Minus;

(3) Plus, contacts 21104, 2105, 2206, lead 24, winding I of relay C12, Minus.

In allotters Jl-102 to VHOS, the blocking relays arranged parallel to relays C11 and C12 are likewise energized.

and

Contacts 25012, 26011 and 75011 are closed. Relay C1 in line allotter L01 is operated through a circuit bypassing finder VZK1, as follows:

(4) Plus, contacts 25012, 26011, lead 76, winding I of relay C1, contacts 1611, 280111, Minus.

Relay C1 opens contacts 2901 and 3601 and closes contact 3101. Contact 3G01 is situated in that chain of contacts through which the subscribers links are made available in incoming calls. It is of no significance in outgoing calls. Contacts 2901 and 3101 are part of the chain of contacts eiective in outgoing calis. Opening of contact 2901 and closing of contact 3101 has the result that the idle subscribers link ZLt1 will not be made available but the neXt link ZLt2 will be. In the event that the selector relay sets accessible to this link via nders VZKI and VNKl (that is, selector relay sets WR7 to WR12 in Fig. l) should likewise be blocked, the relays (not shown) in allotter VHOl corresponding to relays C11 and C12 would be operated. Contacts 32c14 and 33013 of these latter relays (not shown) would be closed so that simultaneously with relay C1, also relay C2 in allotter L01 would operate over conductor 77. Contacts 3402 and 3502 would also be open, and contact 36c2 would be closed. The starting chain for outgoing connections is then transferred to the next-following subscribers link, whose nder starting relay Qv is not shown.

If the selector relay sets of only one group (WR1 to WR3 or WR4 to WR6) are blocked, only one of the relays C11, C12 will be energized. Circuit (4) will not be closed, as in this case the link ZLt1/1-ZLV1 can still reach a selector relay set, such as W'Rl, even though selector relay sets WR1 to WRS are blocked,

Assuming that selector relay set WR1 is idle. Relay Qvl will be energized, which in the case of outgoing calls initiates the connections of the subscribers link ZLtl in both directions, that is, both with a subscribers line and with a secondary or group link, the circuit being traceable as follows:

(5) Plus, contacts 370111, 3Sg1, 1511, 2901, relay Qvl, relay G1, Minus.

The two relays close a holding circuit:

(6) Plus, contacts 390111, 40,131, 41m/1, relay Qvl, relay G1, Minus.

Circuit (5) is opened at 38g1. Relay P101 is energized as follows:

(7) Plus, relay Plol (windings I and II), contact 42qv1, lead 43, contact 44011, relay Q11, high ohmic resistance W-1`1, Minus.

Relay P101 short-circuits its high ohmic resistance winding I at contact 4Splo1. This causes a blocking potential to be applied to lead 43, so that until relay P101 is released (which takes place when the subscribers line has been switched through to an idle selector relay set), the testing relay of no other link allotter of the main group can operatevif during that time calls should come in and the subscribers links ZLfll, ZLtZI, etc. to ZL5191 which also have access to selector relay sets Vi/R1 to WR, should be idle. The use of these links is thus prevented as long as testing relay Pl01 is energized.

Relay Q11 in group allotter VHOI closes its contacts 46:111, 47q11 and 48q11 which are included in the connecting circuits for selector relays sets WR1 to WR3. By means of Contact 496111, the relay Q11 connects itself to lead 43. At contact 741111 (bottom right of 1Eig. 3b), the winding II of relay C11 is connected inthe circuit.

The selector relay sets of each group are to be put to use in a predetermined sequence. Which of these sets is to be used, is determined by a chain of contacts of the blocking relays C. As selector relay set WRI is assumed to be idle, contact 5201 is closed. The following circuit then exists:

(8) Minus, contacts 50pl01 and 51qv1, winding I of connecting relay K11, contact 46q11, winding I of con- 7 'necting relay K21, winding yI of relay Cwr1,`contact 5201, plus.

Connection of link 1.1ZLv1k with group link 2.`ZLv1 is 'elected'v at contacts 53k11, 54k11 and 55k11. Connection of group link` 2.ZLv1 with selector relay set WR1 takes place at contacts 56k21, 57k21 and 58k21. As selector relay set WRI is idle, only this set can be used, not set WRZ or WR3 even though Athey should be idle, since the connecting circuits extending through the energizing windings of connecting relays K22 and X23 are ynot closed, contacts 1701 and 1802 being open.

Simultaneously with the circuit (8), the auxiliary connecting relay Q1 of subscribers link ZLtl is operated as follows:

(9) Plus, contacts 5912101 and Gqvl, relay Q1, Minus. Relay Q1 applies a potential to those connecting relays of vline iinder LKI which are adapted to connect the subscribers lines withk the links ZLtl. Thus, negative battery is applied by means of contacts 61q1, 62911 to relays K11 and K21 of the illustratedsubscribers lines Tnl and Tn2. As the finder start originates from line T111, connecting relay K1 1 will be operated as follows:

(l) Minus, contact 61q1, winding I of relay K1 1,

contact 11ka1, Plus.

The connection is eiected by closure of contacts 63k11, 64k11 and 65k11. The following holding circuit is thus established:

(l1) Plus, contact 12k-a1, winding Il of relay AR1, cut-off relay TR1, contact 65k11, winding II of connecting relay K11, winding III of relay C1, lead 66, contact Sk11, winding II of connecting relay K11, lead 67 of group link .2.ZLv1, winding III of relay C11, contact 58k21, winding II of connecting relay K21, lead 68, winding II of relay Cwrl, contact 69cwr1, blocking relay O1, Minus.

Cut-off TR1, by opening contacts '71tr1 and 70tr1, disconnects line relay AR1 from the subscribers lineland opens circuit (1) at Contact 6171. Relays Anl and R1 in the link allotter are released. When the finder starting relay Kal releases, the connecting circuit (l0) will be opened at contact 111ml. Opening of contact 127ml causes the call meter Zl to be incorporated in holding circuit (l1), but .the meter is not actuated. The'blocking relay O1 of selector relay set WRI blocksthe latter by opening contact 5201, and it also closes contact 1701 so as to condition the selector relay set WRZ, if idle, for use in following call.

However, before these last-mentioned switching operations take place, and simultaneously with the establishment of circuit (8), a circuit through winding I of relay C1 is closed as follows: l Y

(l2) Plus, contacts 72plo1, 73qv1, winding I of relay C1, contacts 16;-1, 286ml, Minus.

Relay C1 actuates the various chains vof contacts co-ntrolling the finder starting relays Qv (for outgoing traic) and Qe (for incoming traic). However, relay Qv2 cannot operate as contact 38g1 is open.

Release of relays R1 and Anl causes interruption of the holding circuit (6) for relaysVQvl and G1. The interruption of circuit (l2) has no eiect upon the energized condition of relay C1,.as winding III ofthe latter is included in holding circuit (11)( Release of relay Qvl alsoresults in the breaking of circuit (7). This removes the blocking potential from lead 43. Relay Q11 releases, is disconnected from lead 43, and also'opens the finder starting contacts 46q11, 47q11 and 48q11.

If thereafter one of the link Vallotters L02 to L04 makes link 1.ZLv11 or 1 ZLv21 or 12h/'31, corresponding to link 1.ZLv1, accessible, such link can be connected only with group link 2.ZvLv2, since the relay Q12, which initiates connection of this link with vone .of the selector relay sets WR4 to WR6, is the only one to be operated in a circuitV corresponding to circuit (7), being connected to lead 43 by contact 75611.

After selector relay set WRI has been busied, sets W-RZ and VVRS, belonging to the saine '-group, can be used by vsubscribers of line groups TnGr.2 to TnGr.5, as will be evident from Fig. l. These sets are reached via the Ypreselection nal finders to VNKS by multiple wiring indicated in Fig. 3b as VNK2-5. Y v

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to `have protected by Letters Patent.

What'iis claimed is:

l. in a telephone system of the relay type wherein subscriber stations are disposed in subgroups and wherein a plurality of said subgroups are arranged to form line groups and wherein a plurality of said line groups are arranged to form a main group; a plurality of relay switching devices common to said main group for extending calls from subscriber stations belonging to such main group, preselection apparatus for connecting any calling station of any one subgroup with any one of said common switching devices, said preselection apparatus comprising at least one irst and at least one second and at least one third finder, each said finder comprising exclusively coupling relays for performing the operations thereof, first trunk lines extending between said first and i said second finders, second trunk lines extending between said second and third nders, and allotter means disposedrespectively between said rst and second tinders and between said second and third finders for determining the particular trunk lines over which calls are to be extended to said common relay switching devices.

2. A system and cooperation of partsraccording to claim l, wherein said first trunk lines extending between said first and said second finders are disposed nearest to the subscriber stations of a subgroup, said first trunk lines being common to all stations included in such subgroup for connecting the corresponding stations with said second finder,- said second inder having access to said second trunk lines, said second trunk lines being common to all lirst nders of a line group.

3. A system and cooperation of parts according to claim l, wherein said first trunk lines extending between said rst and said second nders are disposed nearest to the subscriber stations of a subgroup, said first trunk lines being common to all stations included in such subgroup for connecting the corresponding stations with said second finder, said second finder having access to said second trunk lines, said second trunk lines being common to all first finders of a line group, each first trunk line beingrconnectible in said second finder with at least two of said second trunk lines.

4. A system and cooperation of parts according to claim l, wherein said rst trunk lines extending between said first and said second finders are disposed nearest to the subscriber stations of a subgroup, said first-trunk lines being common to all stations included in such subgroup for connecting the corresponding stations with said second finder, said second nder having access to said second trunk lines, saidsecond trunk lines being common to all rst linders of a line group, each first trunk line being connectible in said second finder with a number of said second trunk lines which is a multiple of the number of said rst trunk lines.

5. A system and cooperation of parts according to claim l, wherein said rst trunk lines extending between said rst and said second finders are disposed nearest to the subscriber stations of a subgroup, said first trunk lines being common to all stations included in such subgroup for connecting the corresponding stations with said second iinder, said second finder having access to said second trunk lines, said second trunk lines being common to all first finders of a line group, each first trunk line being connectible in said second nder with at least two of said second trunk lines, each second trunk line being connectible in said third nder with at least two of said common switching devices.

6. A system and cooperation of parts according to claim 1, wherein said rst trunk lines extending between said rst and said second iinders are disposed nearest to the subscriber stations of a subgroup, said first trunk lines being common to all stations included in such subgroup for connecting the corresponding stations with said second finder, said second iinder having access to said second trunk lines, said second trunk lines being common to all first nders of a line group, each rst trunk line being connectible in said second finder with a plurality of said second trunk lines, each second trunk line being connectible in said third tinder with a number of said common switching devices which corresponds at least to the number of said line groups.

7. A system and cooperation of parts according to claim l, wherein said rst trunk lines extending between said iirst and said second nders are disposed nearest to the subscriber stations of a subgroup, said iirst trunk lines being common to all stations included in such subgroup for connecting the-corresponding stations with said second nder, said second iinder having access to said second trunk lines, said second trunk lines being common to all first nders of a line group, each tirst trunk line being connectible in said second finder with at least two of said second trunk lines, each second trunk line extending to said third finder in which it is connectible with a number of said common switching devices which is greater than the number of rst trunk lines.

8. A system and cooperation of parts according to claim 1, wherein said common switching devices are subdivided into subgroups, each such subgroup comprising a number of switching devices which is equal to the number of said second trunk lines.

9. A system and cooperation of parts according to claim 1, wherein said common switching devices are subdivided into subgroups, each such subgroup comprising a number of switching devices which is equal to the number of said second trunk lines, the number of second iinders allotted to a line group diiering at most by one from the number of subgroups included in said line group.

10. A system and cooperation of parts according to claim 1, comprising switching circuits for said allotter means, said switching circuits comprising blocking relays for making a rst trunk line accessible only if such trunk line is connectible with an idle one of said common switching devices.

11. A system and cooperation of parts according to claim 1, comprising switching circuits for said allotter means, said switching circuits comprising blocking relays for making a iirst trunk line accessible only if such trunk line is connectible with an idle one of said common switching devices, and conductors for said blocking relays, said conductors by-passing said nders.

12. A system and cooperation of parts according to claim 1 wherein a rst nder is allotted to each subgroup of subscriber stations, such first iinder having access to said first trunk lines, coupling start relay means for governing the connection of said rst trunk lines, switching circuits for said allotter means, said switching circuits comprising blocking relays for making a rst trunk line accessible only if such trunk line is connectible with an idle one of said common switching devices, and contacts controlled by said blocking relays forming a starting chain for controlling said start relay means.

13. A system and cooperation of parts according to claim 1, wherein a rst nder is allotted to each subgroup of subscriber stations, such iirst nder having access to said irst trunk lines, switching control relays in said nders, coupling start relay means for governing the connection of said rst trunk lines, circuit means controlled by said start relay means for governing the operation of said switching control relays, and circuit means 10 controlled by said switching control relays for blocking a seized first trunk line and for preparing for the seizure of another iirst trunk line to be taken into use subsequently.

14. A system and cooperation of parts according to claim 1, comprising in said allotter means a blocking relay for each subgroup of stations, and means for energizing said blocking relay when all first finders in such subgroup have been seized for blocking seizure of a second trunk line.

15. A system and cooperation of parts according to claim 1, wherein each firsttrunk line has access to two groups of second finders, blocking relays for said second finders, said blocking relays governing the seizure of a iirst trunk line dependent on the availability of said common switching devices.

16. A system and cooperation of parts according to claim 1, comprising allotter means for each subgroup of subscriber stations for governing the seizure of idle first trunk lines, a test relay in said allotter means, circuit means for operating said test relay duringthe coupling of an idle iirst trunk line with a second nder, and means controlled by said test relay for inhibiting connection of a first trunk line in other subscriber subgroups which has access to nders included in the group of which the seized nder is a part.

17. A system and cooperation of parts according to claim 1, comprising allotter means for each subgroup of subscriber stations for governing the seizure of idle rst trunk lines, a test relay in said allotter means, circuit means for operating said test relay during the coupling of an idle iirst trunk line with a second iinder, a conductor which by-passes a successive nder, and circuit means controlled by said test relay for placing a potential on said conductor to inhibit connection of a iirst trunk line in other subscriber subgroups which has access to tinders included in the group of which the seized iinder is a part.

18. A system and cooperation of parts according to claim 1, comprising allotter means for each subgroup of subscriber stations for governing the seizure of idle irst trunk lines, a test relay in said allotter means, circuit means for operating said test relay during the coupling of an idle rst trunk line with a second finder, a conductor which by-passes a successive iinder, said test relay having a high resistance winding, means for shunting said high resistance winding upon actuation of said test relay to place a potential on said conductor to inhibit connection of a rst trunk line in other subscriber subgroups which has access to finders included in the group of which the seized finder is a part.

19. A system and cooperation of parts according to claim 1, comprising in said allotter means a blocking' relay for each subgroup of stations, and circuit means for energizing said blocking relay when all rst finders in such subgroup have been seized for blocking seizure of a second trunk line, said circuit means including contacts controlled by said common switching devices.

20. A system and cooperation of parts according to claim 1, comprising in said allotter means a blocking relay for each subgroup of stations, a winding of said blocking relay being disposed in a control conductor of a second trunk line which has access to said common switching devices, and means for energizing said blocking relay when all rst iinders in said subgroup have been seized for blocking seizure of a second trunk line.

References Cited in the iile of this patent UNITED STATES PATENTS 1,251,955 Betulander et al. Ian. 1, 1918 1,269,181 Herink .lune 11, 1918 1,645,972 Ronssean Oct. 18, 1927 2,535,764 Voss et al Dec. 26, 1950 v 

